DE 10 2004 032 535 A1 relates to a battery pack. The battery pack comprises a plurality of rechargeable individual cells which are connected in parallel with one another. Provision is made for the individual cells to be designed or selected in such a way that their internal resistance Ri, increases as the state of charge decreases. In order to avoid complexity involved with wiring, monitoring and bringing individual unbalanced cells out of operation during the discharge and/or charge operations of cell strings connected in parallel with one another, lithium-ion cells with such individual cells whose internal resistance Ri increases as the state of charge of the individual cell decreases, becomes minimal at a state of charge of approximately 80% and increases again as the state of charge increases and, with its trough-shaped characteristic, has a counteracting effect for a further divergence of the states of charge need to be included in a battery pack. With a connected limiting circuit, the battery pack is kept within a voltage range of between 7.5 V to 12.6 V, which is greater than the sum of the minimum operating voltage of series-connected individual cells.
DE 10 2008 002 179 A1 relates to an electrical energy store. Said electrical energy store contains a plurality of identical storage elements, wherein at least two strings of storage elements which are connected to one another in series are provided and the strings are connected in parallel. The parallel interconnection is present at a plurality of points along the strings, wherein each string has at least two storage elements and at least one active or passive component is used for connecting the strings in parallel with one another. Owing to the fact that a series circuit is generally insufficient for increasing the total capacitance and for improving the electricity supply capacity, but a parallel circuit of individual cells which is expedient in this regard results in a nonuniformity of the cell voltage between cells on the same plane which are in parallel with one another, the individual cells need to be balanced. Charge balancing either via a passive resistor or via a switchable field-effect transistor which can bridge at a low resistance or isolate at a high resistance is possible on any of these planes in accordance with DE 10 2008 002 179 A1. A time preset tL for the balancing of the scatter σ(C) of the capacitance and the voltage difference ΔUP of from 0.1 V to 0.5 V is, for a fixed resistance Li cell of 0.04 to 0.07Ω: tL=R*σ(C)/ΔUP. For balancing in 10 minutes, this resistance should be at 0.8Ω.
DE 10 305 638 A1 discloses a method and an apparatus for determining an off-load voltage of a battery. A measuring device in this case measures a connection voltage of the battery off-load in a specific cycle after termination of a charge or discharge operation of the battery, and a detection device detects the measured connection voltage. A calculation device calculates a voltage value to which an exponential approximation expression in the function profile asymptotically approximates as an assumed off-load voltage for the respective time period of the detected connection voltage, wherein the exponential approximation expression has an exponent of −0.5 or approximately −0.5 and is determined on the basis of the connection voltage of the respective time period of a plurality of predetermined time periods. The assumed off-load voltage of a time period in which the difference from the assumed off-load voltage of an adjoining time period becomes minimal is determined as an off-load voltage.
DE 10 341 188 A1 describes a battery arrangement for connection to an electrical load, which battery arrangement comprises a plurality of battery strings connected in parallel which are each constructed from a plurality of galvanic cells connected in series. In this case, a measuring unit for estimating the state of charge is assigned to each battery string, which measuring unit measures values for determining the state of charge of the battery string. An evaluation and control unit is connected to the measuring units for estimating the state of charge and evaluates the measured values. In addition, a plurality of switches are arranged in each case between one of the battery strings and the electrical load and in each case between one of the battery strings and the battery charger.
DE 10 2004 032 535 A1 describes a battery pack comprising a plurality of rechargeable individual cells which are connected in parallel with one another. The individual cells are in this case designed or selected in such a way that their internal resistance (Ri) increases as the state of charge (Lz) decreases. With a connected limiting circuit, in this case the battery pack is limited to a voltage range which is greater than the sum of the minimum operating voltages of the individual cells connected in series.
During manufacture of arrangements which have a parallel circuit of battery cells, the following technical problem arises: if the battery cells have states of charge which deviate slightly from one another, when the cell connectors are applied, generally in the form of flat connecting lugs consisting of a copper or aluminum material, very high balancing currents flow. The flow of these balancing currents relates both to screw-type and cohesive connections. The reason for this is that different electromotive forces of the battery cells are discharged via their very low internal resistances. Mention will be made by way of example for a lithium-ion battery cell of the fact that a 60 Ah battery cell in the region of average states of charge at room temperature for short-term pulse loading has an internal resistance of the order of magnitude of 300 μΩ. If the battery cells at the time of manufacture of the battery have a difference in the state of charge of ±2.5%, this results in differences in the voltage in the region of up to 150 mV. If the cell connectors for producing a parallel connection in the case of two adjoining cells are fitted, balancing currents of the order of magnitude of 250 A result. This can lead to considerable sparking at the connection terminals during manufacture, inter alia, which should be avoided during the manufacturing process for safety reasons.